compiler/utils/swap_space.h

/*
 * Copyright (C) 2014 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef ART_COMPILER_UTILS_SWAP_SPACE_H_
#define ART_COMPILER_UTILS_SWAP_SPACE_H_

#include <stddef.h>
#include <stdint.h>
#include <cstdlib>
#include <list>
#include <set>
#include <vector>

#include <android-base/logging.h>

#include "base/logging.h"
#include "base/macros.h"
#include "base/mutex.h"

namespace art {

// An arena pool that creates arenas backed by an mmaped file.
class SwapSpace {
 public:
  SwapSpace(int fd, size_t initial_size);
  ~SwapSpace();
  void* Alloc(size_t size) REQUIRES(!lock_);
  void Free(void* ptr, size_t size) REQUIRES(!lock_);

  size_t GetSize() {
    return size_;
  }

 private:
  // Chunk of space.
  struct SpaceChunk {
    // We need mutable members as we keep these objects in a std::set<> (providing only const
    // access) but we modify these members while carefully preserving the std::set<> ordering.
    mutable uint8_t* ptr;
    mutable size_t size;

    uintptr_t Start() const {
      return reinterpret_cast<uintptr_t>(ptr);
    }
    uintptr_t End() const {
      return reinterpret_cast<uintptr_t>(ptr) + size;
    }
  };

  class SortChunkByPtr {
   public:
    bool operator()(const SpaceChunk& a, const SpaceChunk& b) const {
      return reinterpret_cast<uintptr_t>(a.ptr) < reinterpret_cast<uintptr_t>(b.ptr);
    }
  };

  using FreeByStartSet = std::set<SpaceChunk, SortChunkByPtr>;

  // Map size to an iterator to free_by_start_'s entry.
  struct FreeBySizeEntry {
    FreeBySizeEntry(size_t sz, FreeByStartSet::const_iterator entry)
        : size(sz), free_by_start_entry(entry) { }

    // We need mutable members as we keep these objects in a std::set<> (providing only const
    // access) but we modify these members while carefully preserving the std::set<> ordering.
    mutable size_t size;
    mutable FreeByStartSet::const_iterator free_by_start_entry;
  };
  struct FreeBySizeComparator {
    bool operator()(const FreeBySizeEntry& lhs, const FreeBySizeEntry& rhs) const {
      if (lhs.size != rhs.size) {
        return lhs.size < rhs.size;
      } else {
        return lhs.free_by_start_entry->Start() < rhs.free_by_start_entry->Start();
      }
    }
  };
  using FreeBySizeSet = std::set<FreeBySizeEntry, FreeBySizeComparator>;

  SpaceChunk NewFileChunk(size_t min_size) REQUIRES(lock_);

  void RemoveChunk(FreeBySizeSet::const_iterator free_by_size_pos) REQUIRES(lock_);
  void InsertChunk(const SpaceChunk& chunk) REQUIRES(lock_);

  int fd_;
  size_t size_;

  // NOTE: Boost.Bimap would be useful for the two following members.

  // Map start of a free chunk to its size.
  FreeByStartSet free_by_start_ GUARDED_BY(lock_);
  // Free chunks ordered by size.
  FreeBySizeSet free_by_size_ GUARDED_BY(lock_);

  mutable Mutex lock_ DEFAULT_MUTEX_ACQUIRED_AFTER;
  DISALLOW_COPY_AND_ASSIGN(SwapSpace);
};

template <typename T> class SwapAllocator;

template <>
class SwapAllocator<void> {
 public:
  using value_type    = void;
  using pointer       = void*;
  using const_pointer = const void*;

  template <typename U>
  struct rebind {
    using other = SwapAllocator<U>;
  };

  explicit SwapAllocator(SwapSpace* swap_space) : swap_space_(swap_space) {}

  template <typename U>
  SwapAllocator(const SwapAllocator<U>& other)
      : swap_space_(other.swap_space_) {}

  SwapAllocator(const SwapAllocator& other) = default;
  SwapAllocator& operator=(const SwapAllocator& other) = default;
  ~SwapAllocator() = default;

 private:
  SwapSpace* swap_space_;

  template <typename U>
  friend class SwapAllocator;

  template <typename U>
  friend bool operator==(const SwapAllocator<U>& lhs, const SwapAllocator<U>& rhs);
};

template <typename T>
class SwapAllocator {
 public:
  using value_type      = T;
  using pointer         = T*;
  using reference       = T&;
  using const_pointer   = const T*;
  using const_reference = const T&;
  using size_type       = size_t;
  using difference_type = ptrdiff_t;

  template <typename U>
  struct rebind {
    using other = SwapAllocator<U>;
  };

  explicit SwapAllocator(SwapSpace* swap_space) : swap_space_(swap_space) {}

  template <typename U>
  SwapAllocator(const SwapAllocator<U>& other)
      : swap_space_(other.swap_space_) {}

  SwapAllocator(const SwapAllocator& other) = default;
  SwapAllocator& operator=(const SwapAllocator& other) = default;
  ~SwapAllocator() = default;

  size_type max_size() const {
    return static_cast<size_type>(-1) / sizeof(T);
  }

  pointer address(reference x) const { return &x; }
  const_pointer address(const_reference x) const { return &x; }

  pointer allocate(size_type n, SwapAllocator<void>::pointer hint ATTRIBUTE_UNUSED = nullptr) {
    DCHECK_LE(n, max_size());
    if (swap_space_ == nullptr) {
      T* result = reinterpret_cast<T*>(malloc(n * sizeof(T)));
      CHECK_IMPLIES(result == nullptr, n == 0u);  // Abort if malloc() fails.
      return result;
    } else {
      return reinterpret_cast<T*>(swap_space_->Alloc(n * sizeof(T)));
    }
  }
  void deallocate(pointer p, size_type n) {
    if (swap_space_ == nullptr) {
      free(p);
    } else {
      swap_space_->Free(p, n * sizeof(T));
    }
  }

  void construct(pointer p, const_reference val) {
    new (static_cast<void*>(p)) value_type(val);
  }
  template <class U, class... Args>
  void construct(U* p, Args&&... args) {
    ::new (static_cast<void*>(p)) U(std::forward<Args>(args)...);
  }
  void destroy(pointer p) {
    p->~value_type();
  }

  inline bool operator==(SwapAllocator const& other) {
    return swap_space_ == other.swap_space_;
  }
  inline bool operator!=(SwapAllocator const& other) {
    return !operator==(other);
  }

 private:
  SwapSpace* swap_space_;

  template <typename U>
  friend class SwapAllocator;

  template <typename U>
  friend bool operator==(const SwapAllocator<U>& lhs, const SwapAllocator<U>& rhs);
};

template <typename T>
inline bool operator==(const SwapAllocator<T>& lhs, const SwapAllocator<T>& rhs) {
  return lhs.swap_space_ == rhs.swap_space_;
}

template <typename T>
inline bool operator!=(const SwapAllocator<T>& lhs, const SwapAllocator<T>& rhs) {
  return !(lhs == rhs);
}

template <typename T>
using SwapVector = std::vector<T, SwapAllocator<T>>;
template <typename T, typename Comparator>
using SwapSet = std::set<T, Comparator, SwapAllocator<T>>;

}  // namespace art

#endif  // ART_COMPILER_UTILS_SWAP_SPACE_H_